1. Field of the Invention
The present invention relates to a device for controlling the content of tobacco on a cigarette manufacturing machine and, more particularly, to a tobacco content control device which is capable of controlling the tobacco content constantly to a predetermined amount, so as to guarantee production of cigarettes having uniform tobacco contents.
2. Description of the Related Art
The reduction of total operating costs is a matter of the utmost importance to cigarette manufacturers, as this is a major factor in improving their profitability. Therefore, extensive studies have been carried out with a view to reducing operating costs as much as possible.
One way of reducing operating costs is to enhance the productivity of the cigarette manufacturing machines. From this viewpoint, technical developments have almost reached the point where a single cigarette manufacturing machine can now produce as many as 8,000 cigarettes per minute.
Another way of reducing operating costs is to reduce the weight of the tobacco content of the individual cigarettes. When recent increases in the price of leaf tobacco are taken into consideration, the above approach can yield vast profits through a slight reduction of the tobacco content of each cigarette. However, unduly large reductions of the tobacco content make it difficult to maintain the required quality. Thus, the approach most widely adapted by cigarette manufacturers has been to reduce irregularities in the weight of the tobacco content of individual cigarettes, thereby decreasing the total amount of tobacco used in cigarette production.
More specifically, in the manufacture of cigarettes as currently carried out, the weight of the tobacco content of the cigarettes and a standard deviation corresponding to irregularities in the measured weight are measured. The standard deviation is added to the minimum allowable weight, to obtain the weight which indicates the minimum acceptable quality, i.e., the target value. The cigarettes are then manufactured on the basis of this target value. Therefore, by reducing irregularities in the tobacco content of the individual cigarettes, the target value in production, i.e., the total weight of tobacco used in cigarette production is necessarily reduced.
In order to reduce irregularities in the tobacco content, it is important to maintain the cigarette manufacturing machines in good operating condition, so as to preclude unintended movement of worn-out mechanical parts. However, the most effective measure, in this regard, is to add a tobacco content control device of high quality to the cigarette manufacturing machine. Accordingly, various conventional devices have been proposed in this connection.
For example, Japanese Patent Publication No. 40-14560 (U.S. Pat. No. 3,288,147) discloses a method of controlling the tobacco content on the basis of air permeability, utilizing the correlation between the weight of the tobacco content and their air permeability. However, this method is adversely affected by variations in the suction pressure, particle size, and composition of the tobacco. These variations tend to disturb the pre-established correlation between the weight and air permeability of the tobacco content. Therefore this method has failed to reduce irregularities in the tobacco content to any significant degree.
U.S. Pat. Nos. 2,937,280 and 2,861,683 disclose methods of controlling the tobacco content on the basis of electrostatic capacitance, utilizing the correlation between the tobacco content and their electrostatic capacitance. These methods are, however, susceptible to the influences of the moisture content of the tobacco and temperature, which bias the correlation between the tobacco content and their electrostatic capacitance. Accordingly, these methods do not contribute to the reduction of irregularities in the tobacco content to any substantial degree, and have almost no practical application.
Still another method of reducing irregularities in the weight of the tobacco content utilizes the correlation between the transmission factor of radiation rays, especially .beta. rays emitted from strontium 90, and the density of the tobacco. The tobacco content is controlled on the basis of the transmission factor of these rays. This method is, however subject to such problems as safety in handling the radiation rays, drifting and the inferior response of an amplifier in a subsequent stage, due to the weakness of the output current of an ionization box which serves as a radiation ray detector. However, since there is a reliable correlation between the transmission factor of radiation rays and the tobacco content, this method is employed in most current cigarette manufacturing machines.
There are many causes for irregularities in the tobacco content of cigarettes, such as eccentricity of a cut tobacco feed drum, slippage of cut tobacco during its suction into a perforated cigarette belt, cluttering of a trimmer, nonuniform wear of a wall for stacking cut tobacco, and slippage during production of cigarettes. For this reason, according to frequency analysis of variations in signals corresponding to densities of stick-like cigarettes, various frequencies, from a low frequency of 0.001 Hz (long variation cycle) to a high frequency of 10 Hz or 100 Hz (short variation cycle), are continuously included, and thus a so-called "white noise" state results therefrom.
In order to reduce irregularities in the tobacco content of cigarettes, a fast response control device may be used to eliminate variations in density signals representing speeds lower than the response speed.
In the 1950s, a tobacco content control device utilizing a radiometric density detector was proposed for the above purpose. Extensive studies have been carried out since then, to improve the response speed of the device.
A device for controlling the tobacco content of cigarettes by utilizing radiation rays is described in U.S. Pat. No. 2,954,775. This device employs a method of controlling the feed speed of a cut tobacco feeder on the basis of a signal from the radiometric density detector. According to this method, however, the speed of a feeder having a large inertia must be controlled. Consequently, the response rate cannot be increased to a specific or higher value. As a result, the only weight variations eliminated using this device, are those corresponding to a low frequency of about 0.01 Hz or less.
In order to increase the response speed, Japanese Patent Publication No. 38-15949 (U.S. Pat. No. 3,089,497) proposes a method of controlling a transferred tobacco layer on the basis of a signal from a radiometric density detector. According to this method, a drive motor is rotated in the forward/reverse direction to move the trimmer, in order to control the amount of tobacco. The trimmer presents a relatively small inertia when it is moved. In addition, the time interval (i.e., the delay time) from weight change detection by the radiation ray detector to the driving of the trimmer is relatively short. For these reasons, a response speed higher than is attainable by use of other methods can be obtained, in this case, with variations in frequencies of 0.1 Hz or less being almost entirely eliminated. Consequently, this method is employed in most current cigarette manufacturing machines.
Japanese Patent Publication No. 51-95198 (U.S. Pat. No. 4,036,238) proposes a method of utilizing an electrohydraulic servo mechanism for moving the trimmer up and down, instead of the motor for driving the trimmer which is disclosed in the above-described method. According to the improved method, weight variation corresponding to a low frequency of about 0.5 Hz or less can be eliminated.
U.S. Patent Application Serial No. 705,877, filed Feb. 27, 1985 (corresponding to Japanese Patent Disclosure (Kokai) No. 60-234574 and EPC Laid Open Publication No. 160,799) proposes a method of minimizing the delay time by arranging another radiometric density detector immediately behind the trimmer. This method permits the elimination of variations in frequencies of 1 Hz or less.
However, development of these high-speed devices has, instead of satisfying demand, merely created further, strong demand for the development of a tobacco content control device of even higher speed and higher performance.